This application claims the priority of German patent application no. 196 47 660.7, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a triggering device for occupant restraint systems in a vehicle for protecting vehicle occupants in a collision.
A triggering device of this type, disclosed in German patent document DE 43 24 753 A1, comprises a triggering control device which triggers a side airbag when a triggering threshold is exceeded by a delay signal generated from the acceleration signal of a transverse acceleration sensor. Also, a deformation sensor located behind the outer skin in the side area of the vehicle detects the deformation rate of the outer skin during an impact. In the event of critical deformation, a control signal is delivered to lower the triggering threshold by an amount which increases directly with the determined deformation rate. Alternatively (or in addition), the triggering readiness can also be influenced by changing the generation of the delay signal as a function of the deformation rate.
This known triggering device permits a rapid and safe response of the triggering device in the event of a side impact which is dangerous to occupants, and at the same time provides security against improper triggering in collisions that are not too dangerous. The known triggering device can be considered disadvantageous, however, in situations when the extensive monitoring of one side of the vehicle by means of deformation sensors can be implemented only at great expense.
In addition, a number of devices are known in which the decision to trigger restraining devices is not based on the evaluation of an acceleration signal from an acceleration sensor. Rather an attempt is made, for example by means of proximity sensors, even before any impact, to detect relevant collision parameters (such as spacing and relative speed), in order to anticipate an unavoidable impact, and to activate corresponding safety equipment even before the collision. Because triggering takes place early, a restraint system such as an airbag has more time to deploy, permitting gentler impact protection for the occupants. This type of advance triggering is referred to as "pre-crash" triggering. The emphasis then is on the possibility of avoiding the impact even before an impending impact, initiating anti-collision strategies such as automatic emergency braking or avoidance maneuvers.
This general idea is implemented in detail in German patent document DE 36 37 165 A1. At least one transmitter that preferably emits electromagnetic signals in the direction of travel, and at least one receiver that picks up at least one echo signal reflected from the object, are used as a sensor system for locating a collision object. Relative speed with respect to the collision object can be determined directly from the Doppler frequency shift of a radar or infrared signal. For further details and more information on the prior art of pre-crash triggering with the radar method and the radar-Doppler method, reference is made to German patent documents DE 22 24 842 A1, DE 44 24 878 A1, and DE 44 26 090 A1; International patent document WO 86/05149; European patent document 210 079 A2; and U.S. Pat. Nos. 4,104,682 and 3,684,309.
Radar-Doppler methods are also suitable for road condition detection. In a method disclosed for example in German patent document DE 44 29 419 A1, the power density spectrum of the ground echo from a radar-Doppler system is evaluated.
German patent document DE 36 37 165 A1, mentioned above, teaches the use of video camera systems with image evaluation, instead of radar or infrared sensors. By image processing, the distance, rate of approach, size, and shape of an approaching object are determined, compared with stored data or samples, and the degree of danger is evaluated. If a predetermined danger threshold is exceeded, an airbag is triggered. Further technical details for a system for monitoring the vehicle-external state using video cameras also follow from German patent document DE 43 08 776 A1.
Pre-crash triggering systems are known in which, in the near area between two vehicles on a collision course, collision-relevant data such as weight, speed, and direction are exchanged over a wireless communication space.
Known pre-crash triggering devices include object detection arrangements that make it possible reliably to detect an oncoming vehicle and determine its relative speed. The degree of danger of an imminent collision however also depends critically on the weight of the object with which the collision will occur. At least with the less expensive method that uses radar or infrared signals to detect the collision object, this important information cannot be obtained and the triggering decision cannot be based on it. A large cardboard carton lying on the road could therefore be evaluated in the same way as a standing vehicle and elicit a corresponding but inappropriate reaction in this case.
In order for the known systems to offer the best possible protection in pre-crash triggering, even against collisions with objects at rest such as posts or trees, the latter must also be recognized by the object detection system. As far as sensing is concerned, this requires a sensitive and continuous design of the system which in turn increases the danger of improper triggering caused for example by a passing vehicle coming in the other direction at a short distance.